Is this a common Vaillant problem?

[Post and beam]

I have to restore pressure every day or every other day on my installation, by about half a bar to be accurate. Only been in the house for one month and had assumed this was air gradually settling out of the system. Although it never seems to appear anywhere.

But, i saw on a facebook page today that someone asked about a very similar scenario and was told that this is a known issue with Vaillant arotherm heat pumps. Mine is a 5Kw version.

Lots of Vaillant user on here so my question is, is this a widely known issue?

[JamesPa]

50 minutes ago, Post and beam said:

I have to restore pressure every day or every other day on my installation, by about half a bar to be accurate. Only been in the house for one month and had assumed this was air gradually settling out of the system. Although it never seems to appear anywhere.

But, i saw on a facebook page today that someone asked about a very similar scenario and was told that this is a known issue with Vaillant arotherm heat pumps. Mine is a 5Kw version.

Lots of Vaillant user on here so my question is, is this a widely known issue?

I cant see that this is anything  special to Vaillant, its more likely the pipework system itself, and more to the point the water in it.

 

It took a month for the air in my 7kW Vaillant based system fully to come out of solution.  Some came out through the automatic bleed valves, but there was one radiator which had to be bled every two days for a month because air collected there.   Needless to say it needed topping up after air was bled.   My installer had been diligent and run a purge cycle which shifts air not in solution, but does nothing to shift small bubbles of which there will be many.  Patience is required! 

 

That said it sounds like you could have a slow leak, which might of course be anywhere in pipework which has been disturbed or at a faulty/leking an automatic air vent/pressure release valve.  I know that pressure release valves occasionally get stuck although I thought this happened only as they age - but maybe it can happen to new ones.  Interestingly my installer visited last week for the first annual service and closed the automatic air vent in the outdoor unit which apparently is a Vaillant recommendation at the first annual service and suggests that they can eventually leak.

 

If the problem persists then it does need to be traced. 

 

I dont know if that helps, just my personal experience

Edited yesterday at 09:37 by JamesPa

[Post and beam]

23 minutes ago, JamesPa said:

 Needless to say it needed topping up after air was bled.

This is the kicker, i have not been bleeding mine every time. It needs topping up , and much too frequently. Which led me to believe it was a leak.

No signs of water leaking inside the house and i certainly hope there are no issues between the floors with all the joints. I would expect to see patches on the ceiling if this were the case.

If it stops raining i might be able to monitor the unit outside for damp patches.

[JamesPa]

Just now, Post and beam said:

This is the kicker, i have not been bleeding mine every time. It needs topping up , and much too frequently. Which led me to believe it was a leak.

No signs of water leaking inside the house and i certainly hope there are no issues between the floors with all the joints. I would expect to see patches on the ceiling if this were the case.

If it stops raining i might be able to monitor the unit outside for damp patches.

OK fair diagnosis IMHO.  

 

My gas boiler based system exhibited this behaviour in its failing days, turned out to be the pressure release valve in the boiler.  I also, at times, had the odd leaky compression joint elsewhere in the system although they tended to self heat because of how hard our water is!

 

You could take the side and front off of the unit, the AAV is certainly obvious in my 7kW machine, I dont know if there is also a PRV but I imagine so!

[Beau]

Our 7kw model has not suffered any drop in pressure in normal running but we've only had it a year.  I hadn't noticed it mentioned on the owners group but then I've not been looking out for it either.

 

 

[Dillsue]

If you close all the auto air vent valves so no further air can be expelled that should eliminate them as a source of leakage. Disconnect any vent pipework on your pressure relief valve and push a couple of sheets of toilet paper into the PRV vent so you can see if that's leaking. Repressurise and if you're still loosing pressure you've likely got a leak!!

[Post and beam]

1 hour ago, Dillsue said:

close all the auto air vent valves

If i knew where and how many i could do this.

 

1 hour ago, Dillsue said:

into the PRV

Do you mean the tundish?

[sharpener]

4 hours ago, JamesPa said:

You could take the side and front off of the unit, the AAV is certainly obvious in my 7kW machine, I dont know if there is also a PRV but I imagine so!

 

Certainly worth doing, I have read on the FB forum several instances of leaking PRVs (IIRC related to a change of supplier, no doubt chasing a few p).

While you have the covers off there is a cable run where my Vaillant service man put a drip loop to stop water sliding down on to a pcb, apparently this is an undocumented mod.

 

I topped up to 1.5 bar 10 days ago and it is back down to 1.3, seems to go down by a further 0.2 in use (sensor is on suction side of main pump) but have not been able to find a leak so just put up with it.

 

[JamesPa]

6 hours ago, Post and beam said:

7 hours ago, Dillsue said:

close all the auto air vent valves

If i knew where and how many i could do this.

 

7 hours ago, Dillsue said:

into the PRV

Do you mean the tundish

No.  That's linked to the pressure in the hot water tank not the pressure in the heating system.  They are separate pressure vessels.

[IGP]

Sounds like a leak. I had this on some untested pipework in our extension, the system kept losing pressure about 0.5 bar a day. Turned out to be a mangled o-ring in a push fit elbow. Thankfully the floor where it was hadn’t been finished and was easy to lift. 

[JamesPa]

@Post and beam

Hopefully from the various replies above you get the impression that this isn't an ashp specific problem, it's a central heating problem, which may lie in the ashp, or may not (just as a similar problem in a system with a gas boiler may lie in the boiler or may not).

 

Unfortunately such problems can be a little difficult to track down, but there is no realistic alternative.  Also unfortunately you now have the task of tracking it down or paying others to do so, unless it turns out that it's a warranty problem.  

 

I know this isn't the ideal situation, but it is the realistic one.

 

I suggest some investigation unless you prefer to pay others to find the problem if it turns out not to be covered by warranty.  I'm sure people here will continue to provide hints as to how to diagnose the fault if you want to track it down yourself.

 

 

Edited 23 hours ago by JamesPa

[Dillsue]

On 02/12/2025 at 12:10, Post and beam said:

Do you mean the tundish?

If the tundish is very close to the PRV then yes. If it's a few metres away then personally I'd push it into the PRV vent. If the pipe between PRV and tundish is long and warm you've got the chance of any leaking water evaporating so you'll see nothing in the tundish

[Dillsue]

On 02/12/2025 at 18:45, JamesPa said:

No.  That's linked to the pressure in the hot water tank not the pressure in the heating system.  They are separate pressure vessels.

?? There's likely auto air vents on the HP circuit and almost certainly if its a pressurised system??